1. Field of the Invention
This invention pertains to intraoperative monitoring methods and devices, and more particularly to intraoperative monitoring devices and methods for monitoring temperature-induced changes to tissue with high resolution digital X-ray imaging and inducing the changes to the tissue.
2. Discussion of Related Art
Various types of thermotherapy have been considered, and/or applied to the treatment of cancers. Laser interstitial thermotherapy (LITT) has received attention as a surgical procedure for the treatment of cancer tumors, and particularly with respect to liver, head, neck and breast cancer.
Laser interstitial thermotherapy is a surgical procedure for the treatment of cancer tumors in which near infra-red laser energy is delivered to the tumor site inside the body through a flexible fiber-optic probe. Some fiber optic probes in use terminate with a light diffusing tip. The infra-red laser radiation is absorbed by the tumor cells, which results in a temperature increase and subsequent cell death of the tumor cells. The temperature distribution around the light-diffusing tip, and thus the extent of cell-death, is a function of the laser parameters, treatment time, tumor size, and shape, fiber optic tip geometry, optical properties of the tumor, and blood perfusion rates in both compressed and uncompressed treatment sites.
The treatment parameters (e.g., wavelength, power, duration, tip geometry, and tip location and orientation) must be selected so as to minimize collateral damage to healthy tissue surrounding the tumor, yet still must ensure reliable total tumor destruction. Because of tissue inhomogeneities, and inter-patient variability of the physical and biological properties of tumors, intraoperative monitoring of the treatment effect is highly desirable. Currently, intraoperative monitoring of LITT is conducted with magnetic resonance imaging (MRI) or three-dimensional ultra-sound, or by measuring the temperature at discrete locations in-situ with thermocouples or thermo-sensing fluorescent probes.
Intraoperative monitoring with MRI has numerous disadvantages which include being expensive and not being able to be used with metal protected light guides which are currently used for the LITT probe. Three-dimensional ultra-sound imaging techniques are currently at an experimental stage and have not been sufficiently developed. In situ thermo-couples or fluorescence-based temperature probes only provide temperatures at a relatively small number of points throughout the tissue being monitored. Currently, only fluorescence-based temperature probes are approved by the FDA for clinical use.
It is thus an object of this invention to provide an intraoperative monitoring device and method used in conjunction with diagnostic procedures.
It is another object of this invention to provide an intraoperative monitoring device and method used in conjunction with stereotactic X-ray mammography.
It is another object of this invention to provide an intraoperative monitoring method and device that provides a high resolution X-ray image of temperature-induced changes to tissue during thermotherapy.
It is another object of this invention to provide an intraoperative monitoring device and method that provides a high resolution temperature map of tissue during thermotherapy.
It is another object of this invention to provide a method of thermotherapy which includes real-time monitoring of temperature induced changes to tissue during thermotherapy using X-ray imaging for feedback information used during the thermotherapy.
The above, and related objects of this invention are realized by providing a device for monitoring thermally-induced changes to localized regions of tissue which has an X-ray illumination source, an X-ray detector, a data storage unit in communication with the X-ray detector, an image comparison unit in comparison with at least the data storage unit and an image display unit in communication with the image comparison unit. The X-ray illumination source and the X-ray detector are arranged to reserve a space therebetween for accommodating tissue to be monitored. Preferably, the tissue to be monitored is a portion of a patient""s body which is being monitored during the surgical procedure. The X-ray detector produces a plurality of X-ray image data signals, each of which corresponds to an X-ray image of the portion of the patient""s body being monitored. Preferably, the X-ray detector produces a digital X-ray image data signal. The X-ray image data signal corresponds to a two-dimensional image of the portion of the patient""s body being monitored in a preferred embodiment, and corresponds to a three-dimensional X-ray image of the portion of the patient""s body in another preferred embodiment.
The image comparison unit compares X-ray image values between corresponding spatial points of first and second X-ray image signals to provide a resultant X-ray image signal based on the comparison. Preferably, the image comparison unit subtracts pixel values between corresponding spatial points of first and second X-ray image signals, providing a measure of the change in intensity of the received X-ray signal at each point within the digital X-ray image signals. The resultant image signal is then one particular example of a difference image signal that is generated by the image comparison unit and then displayed on an image display unit to provide real-time information concerning the temperature distribution and changes in temperature throughout the portion of the patient""s body being monitored. The images also provide information corresponding to the volume of denatured tissue. In the preferred embodiment, both the data storage unit and image comparison unit are implemented within a personal computer or workstation.
Another preferred embodiment of the present invention is directed to a device for causing thermally-induced changes to localized regions of tissue. The device according to this preferred embodiment has an X-ray illumination source, an X-ray detector, a data storage unit in communication with the X-ray detector, a thermotherapy heating assembly, an image comparison unit in communication with at least the data storage unit and an image display unit in communication with the image comparison unit. The combination of X-ray illumination source, X-ray detector, data storage unit, image comparison unit, and image display unit are constructed and arranged in a manner similar to the monitoring device summarized above. The thermotherapy heating assembly may be selected from currently known devices and may include a laser irradiation devices, microwave irradiation devices, radio frequency irradiation device, or an ultra-sound energy source. In the preferred embodiment, the thermotherapy heating assembly is a laser interstitial thermotherapy assembly. There are laser interstitial thermotherapy assemblies known in the art that are suitable for use with the device for causing thermally-induced changes to localized regions of tissue, in accordance with this invention. For example, the laser interstitial thermotherapy devices described in Robinson, David S. et al, xe2x80x9cInterstitial Laser Hyperthermia Model Development for Minimally Invasive Therapy of Breast Carcinomaxe2x80x9d, J. Am Coll Surg, 1998, reprint pages 284-292; Milne, Peter J. et al, xe2x80x9cDevelopment of Stereotactically Guided Laser Interstitial Thermotherapy of Breast Cancer: In Situ Measurement and Analysis of the Temperature Field in Ex Vivo and In Vivo Adipose Tissue,xe2x80x9d Lasers in Surgery and Medicine, 2000, reprint 26:67-75; and Manns, Fabrice et al, xe2x80x9cIn Situ Temperature Measurements With Thermocouple Probes During Laser Interstitial Thermotherapy (LTT): Quantification and Correction of a measurement Artifact,xe2x80x9d Lasers in Surgery and Medicine, Vol. 23, No. 2, 1998, reprint pages 94-103 are suitable: the entire content of each is incorporated herein by references.
Another preferred embodiment of this invention is directed to a method of thermally inducing and monitoring changes to localized regions of tissue, including illuminating a volume of tissue with a first beam of X-rays, detecting portions of the first beam of X-rays that pass through localized regions of tissue within the volume of tissue, generating a first X-ray image signal from the portions of the first X-ray beam detected, and applying heat to at least a localized region of tissue within the volume of tissue. A preferred embodiment of the method is directed to thermally inducing and monitoring changes to tumors in breast cancer patients. After applying the heat, the volume of tissue is illuminated with a second beam of X-rays. X-rays from a second beam of X-rays that pass through the volume of tissue that includes the localized regions, e.g., through the tumors, are detected and a second X-ray image signal is generated therefrom. In the preferred embodiment, the first X-ray image signal is stored in a data storage unit and then retrieved for generating a resultant image signal which preferably is a difference image signal based upon a comparison of the first and second X-ray image signals. In a preferred embodiment, the first and second X-ray image signals and the difference image signal are digital signals and the difference image signal is formed by subtracting each pixel value of the first X-ray image signal from a spatially corresponding pixel of the second X-ray image signal. Each X-ray image signal is correlated with the detected X-ray intensity corresponding to the particular spatial point, and the difference image signal corresponds to an intensity change in the detected X-rays for each corresponding difference image point. The difference image signal is rendered as a difference image and displayed on an image display device, preferably, to provide real-time feedback to the surgeon applying thermotherapy. The surgeon can then determine whether to alter the thermotherapy parameters, maintain the thermotherapy, or terminate the thermotherapy with the aid of the temperature change information displayed on the image display device.
If the surgeon decides to continue the thermotherapy, the volume of tissue is illuminated with a third beam of X-rays. (The X-ray beams may be along the same or modified paths relative to the volume of tissue.) The X-rays from the third beam that pass through the volume of tissue are detected and a third X-ray image signal is generated therefrom. The second and third beam of X-rays may be separated in time by a period in which there is no illumination of X-rays, or it may be a continuous illumination classified as contiguous time periods. Continuous illumination is currently less preferable than intermittent illumination due to safety concerns regarding the total X-ray dose applied to the patient.
The first X-ray image signal is again retrieved from the data storage unit and used as a static reference image signal to produce a second difference image signal by subtracting each corresponding pixel of the first and second image signals. The second difference image signal is then rendered and displayed as an updated difference image which provides updated information to the surgeon, preferably in real time. The surgeon can then use the temperature change information displayed to reassess the status of the thermotherapy to determine whether to alter, continue or terminate the thermotherapy.
This process is repeated until the surgeon determines that the thermotherapy should be terminated. In this embodiment, the difference image signal is always generated by retrieving the same static reference image signal from the data storage unit and subtracting it from the updated measurement signal.
The above detailed description of a succession of measurements is by way of example. The reader should recognize from the teachings herein that the scope and spirit of the invention includes the general concepts and not the particular order of observing and responding to the observations.
In an alternative embodiment, all method steps are the same as those noted above, except that a static reference image signal is not used to generate the difference image signal. In this preferred embodiment, the first X-ray image signal is replaced by the second X-ray image signal after the first difference image signal is generated. Similarly, the second X-ray image signal stored in the data storage unit is replaced with the third X-ray image signal after the second difference image signal is generated. This process is repeated until the surgeon determines that the thermotherapy should be terminated. This case provides a dynamic reference image signal for forming the difference image signal in which the dynamic reference image signal is updated after each succeeding illumination.
In alternative embodiments, one may combine both static and dynamic processes for generating the difference image signals. For example, the reference image signal may be maintained in memory without being replaced for one, two or more successive illuminations, followed by being updated either frequently, such as with a pure dynamic reference image signal, or intermittently, again being a mix of dynamic and static processes.
Another embodiment of the invention is directed to a method of destroying cancerous tissue by forming a first X-ray image of a portion of a patient""s body, applying heat to a localized region of the portion of the patient""s body, forming a second X-ray image of the portion of the patient""s body subsequent to applying heat to the localized region of the portion of the patient""s body, and generating a difference image based on a comparison of the first X-ray image data to the second X-ray image data. The surgeon then modifies the application of heat based on information obtained from the difference image. In a preferred embodiment, the first and second X-ray images and the difference X-ray image are high resolution, three-dimensional digital X-ray images. Preferably, the comparison is a subtraction of the first X-ray image from the second X-ray image. The illumination with successive X-ray beams, detecting, generating X-ray image signals, and generating successive difference image signals is repeated as the surgeon requires until he terminates the thermotherapy.